Initiation of biological control against Parthenium hysterophorus L. (Asteraceae) in South Africa.
The annual herbaceous plant, Parthenium hysterophorus L. (Asteraceae) (parthenium), has been a major weed of global significance for several decades, with wide-ranging impacts on agriculture, biodiversity conservation, and human and animal health. Despite this, in 2003, South Africa became the first African country and only the third country worldwide to implement a biological control programme against the weed. It seems that a suite of agents is needed to achieve effective biological control of parthenium under different environmental conditions and in different regions. The rust fungus, Puccinia abrupta Dietel & Holw. var. partheniicola (H.S. Jacks.) Parmelee (Pucciniales: Pucciniaceae), is already present in South Africa. Three agents have been imported and evaluated, namely the leaf rust fungus Puccinia xanthii Schwein. var. parthenii-hysterophorae Seier, H.C. Evans & Á. Romero (Pucciniales: Pucciniaceae), which was released in 2010, and both the leaf-feeding beetle Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae: Cassidinae) and the stem-boring weevil Listronotus setosipennis (Hustache) (Coleoptera: Curculionidae), for which permission to release is being sought. A stem-galling moth Epiblema strenuana (Walker) (Lepidoptera: Tortricidae), seed-feeding weevil Smicronyx lutulentus Dietz (Coleoptera: Curculionidae), and stem-boring moth Carmenta nr. ithacae (Beutenmüller) (Lepidoptera: Sesiidae) are also under consideration. Studies conducted in South Africa prior to the release of biological control agents, demonstrated an extensive, but highly variable, soil seed bank. In 2005, the South African biological control programme was extended to Ethiopia through an international cooperative programme. Parthenium has the potential to become more widespread and problematic in sub-Saharan Africa, and the implementation of biological control could assist in reducing this risk.